Systematic exploitation of thermotropic bicontinuous cubic phase families from 1,2-bis(aryloyl)hydrazine-based molecules

Stabilization of Bicontinuous Cubic Phase and Its Two-Sided Nature Produced by Use of Siloxane Tails and Introduction of Molecular Nonsymmetry

A recent intriguing finding that a helical network arrangement forms the bicontinuous cubic phase is attracting great attention for the possibility of new routes to asymmetric synthesis by achiral molecules. However, the design of the molecular structure for the cubic phase is still unrevealed. In this work, a nonsymmetric core molecule with larger naphthalene and smaller benzene moieties at each side of the central linkage and the same disiloxanyldecyloxy terminal at both terminals is shown to be the first example of molecule forming both single-layered and double-layered core assembly modes in the Ia3d phase as a single molecule system. The molecule forms the former mode at high temperatures as a thermodynamically stable phase, similarly to the symmetric naphthalene core system, whereas, on cooling below a temperature (∼350 K), a metastable Ia3d phase forms a double-layered core state down to room temperature, which is common to the benzene core system. As another effect of the nonsymmetric core, the cubic phase is maintained at room temperature for more than 100 days with slight distortion. Infrared spectral studies and quantum chemical calculations suggested the easy transformation between the two core assembly modes. The core nonsymmetry can be a versatile fine-tuning of the core assembly mode and phase stability for the cubic phase molecules.

Controlling Mirror Symmetry Breaking and Network Formation in Liquid Crystalline Cubic, Isotropic Liquid and Crystalline Phases of Benzil-Based Polycatenars

Spontaneous development of chirality in systems composed of achiral molecules is important for new routes to asymmetric synthesis, chiral superstructures and materials, as well as for the understanding of the mechanisms of emergence of prebiotic chirality. Herein, it is shown that the 4,4'-diphenylbenzil unit is a universal transiently chiral bent building block for the design of multi-chained (polycatenar) rod-like molecules capable of forming a wide variety of helically twisted network structures in the liquid, the liquid crystalline (LC) and the crystalline state. Single polar substituents at the apex of tricatenar molecules support the formation of the achiral (racemic) cubic double network phase with Ia 3 ‾ d symmetry and relatively small twist along the networks. The combination of an alkyl chain with fluorine substitution leads to the homogeneously chiral triple network phase with I23 space group, and in addition, provides a mirror symmetry broken liquid. Replacing F by Cl or Br further increases the twist, leading to a short pitch double gyroid Ia 3 ‾ d phase, which is achiral again. The effects of the structural variations on the network structures, either leading to achiral phases or chiral conglomerates are analyzed.

Mirror Symmetry Breaking in Liquids and Their Impact on the Development of Homochirality in Abiogenesis: Emerging Proto-RNA as Source of Biochirality?

Recent progress in mirror symmetry breaking and chirality amplification in isotropic liquids and liquid crystalline cubic phases of achiral molecule is reviewed and discussed with respect to its implications for the hypothesis of emergence of biological chirality. It is shown that mirror symmetry breaking takes place in fluid systems where homochiral interactions are preferred over heterochiral and a dynamic network structure leads to chirality synchronization if the enantiomerization barrier is sufficiently low, i.e., that racemization drives the development of uniform chirality. Local mirror symmetry breaking leads to conglomerate formation. Total mirror symmetry breaking requires either a proper phase transitions kinetics or minor chiral fields, leading to stochastic and deterministic homochirality, respectively, associated with an extreme chirality amplification power close to the bifurcation point. These mirror symmetry broken liquids are thermodynamically stable states and considered as possible systems in which uniform biochirality could have emerged. A model is hypothesized, which assumes the emergence of uniform chirality by chirality synchronization in dynamic “helical network fluids” followed by polymerization, fixing the chirality and leading to proto-RNA formation in a single process.

Double-Gyroid Nanostructure Formation by Aggregation-Induced Atropisomerization and Co-Assembly of Ionic Liquid-Crystalline Amphiphiles

We report a new molecular‐design principle for creating double‐gyroid nanostructured molecular assemblies based on atropisomerization. Ionic amphiphiles containing two imidazolium rings close to each other were designed and synthesized. NMR data revealed that the rotation of the imidazolium rings is restricted, with an activation energy as high as 63 kJ mol⁻¹ in DMSO‐d₆ solution (DFT prediction for a model compound in the vacuum: 90–100 kJ mol⁻¹). Due to the restricted rotation, the amphiphiles feature “double” atropisomeric axes in their ionic segments and form three stable atropisomers: meso, R, and S. These isomers co‐organize into Ia3‾d ‐type bicontinuous cubic liquid‐crystalline mesophases through nanosegregation of the ionic and non‐ionic parts. Considering the intrinsic characteristic of Ia3‾d ‐type bicontinuous cubic structures that they are composed of intertwined right‐ and left‐handed single gyroids, we propose that the simultaneous presence of both R‐ and S‐atropisomers is an important contributor to the formation of double‐gyroid structures.

Molecular design of anti-spindle-like molecules by use of siloxanyl terminals for a thermotropic bicontinuous cubic phase

By modifying the three molecular moieties, siloxane terminal, alkyl spacer, and aromatic core part, the molecular requirements for the formation of bicontinuous cubic phases are presented.

Molecular packing in two bicontinuous Ia3[combining macron]d gyroid phases of calamitic cubic mesogens BABH(n): roles in structural stability and reentrant behavior

1,2-Bis(4'-n-alkoxybenzoyl)hydrazine [BABH(n), n is the number of carbon atoms in the alkyl chain] exhibits two different Ia3[combining macron]d cubic phases depending on the chain length (5 ≤n≤ 13 and 15 ≤n≤ 22). The molecular packing modes, not only of molecular cores but also of alkyl chains, are investigated through a maximum entropy method (MEM) and an analysis of the chain-length dependence of the body diagonal of the unit cell. The analyses revealed the difference in molecular packing. The short-chain Ia3[combining macron]d structure of BABH(n) (5 ≤n≤ 13) is constructed by single-layered core motifs and bilayers of alkyl chains, in which the orientation is tilted from the normal to the layer. The long-chain Ia3[combining macron]d structure (15 ≤n≤ 22) is formed by double-layered core motifs and monolayers of alkyl chains, in which the orientation is normal to the layer. Based on the molecular packing modes, the reentrant behavior between the two Ia3[combining macron]d phases was clarified. It was revealed that the alkyl chains of BABH(n) molecules play an essential role in the formation and stability of the two Ia3[combining macron]d structures.